Novel Antischistosomal Agent

ABSTRACT

An object of the present invention is to provide a novel antischistosomal agent, and more specifically, to provide a novel drug capable of inhibiting a growth of schistosomes in vivo to prevent development of liver dysfunction due to eggs of the schistosomes in the case of infection with the schistosomes. The novel antischistosomal agent includes as an active ingredient a peroxide derivative. Specifically, the novel antischistosomal agent includes as an active ingredient a peroxide derivative represented by the general formula (I): 
     
       
         
         
             
             
         
       
     
     where C represents an alicyclic hydrocarbon ring group which may be substituted, and n represents an integer of 1 to 6.

TECHNICAL FIELD

The present invention relates to a novel compound useful for theprophylaxis and treatment of schistosomiasis, and more specifically, toa novel drug capable of killing schistosomes, and when the schistosomescannot be killed, inhibiting the growth of the schistosomes dependinggrowth stages in vivo to prevent the development of liver dysfunctioncaused by worms' eggs in the case of infection with the schistosomes.

The present application claims the priority of JP 2008-0172663, which ishereby incorporated by reference.

BACKGROUND ART

Schistosomiasis is a disease caused by the parasitism of adultschistosomes in the veins and is broadly classified into urogenitalschistosomiasis and intestinal schistosomiasis. An example of theurogenital schistosomiasis is schistosomiasis haematobia (pathogen:Schistosoma haematobium) and examples of the intestinal schistosomiasisinclude schistosomiasis mansoni (pathogen: S. mansoni), schistosomiasismekongi (pathogen: S. mekongi), and schistosomiasis intercalatum(pathogen: S. intercalatum) as well as schistosomiasis japonica(pathogen: S. japonicum). Infection of humans with schistosomes occurswhen the humans go into fresh water, for example, a river, a lake, or amarsh. The World Health Organization estimates that 200,000,000 peoplesuffer from the disease worldwide, and the number of people died ofsevere complications associated with the disease is estimated to beannually 20,000 or 200,000, which varies from report to report.Schistosomiasis haematobia is distributed in Middle East, wide range ofareas in Africa including Madagascar, and Mauritius, and schistosomiasismansoni is distributed in, for example, the Arabian Peninsula, most ofAfrican countries located north of the equator (Egypt, Libya, Sudan,Somalia, Mali, and Senegal), Mauritius, Brazil, some of variousCaribbean countries, Surinam, and Venezuela. Schistosomiasis japonica isdistributed in, for example, the Yangtze valley in China, Philippines,and the island of Sulawesi in Indonesia, schistosomiasis mekongi isdistributed in the Mekong river basin in Cambodia and Laos, andschistosomiasis intercalatum is locally distributed in West and CentralAfrica.

Also in Japan, there were several areas endemic for schistosomiasisjaponica in the past. However, the execution of an eradication projectincluding land-use alteration and measures for intermediate hosts aswell as community education and mass examination has contributed to adrastic decrease in the number of infected people. As a result, therehas been no report on people newly infected with Schistosoma japonicumsince 1976 in Japan.

Information about the kinds of pathogens, life cycles of pathogens,clinical symptoms of infectious diseases, pathological diagnosis, andthe like for schistosomiasis is described in detail in the homepage ofInfectious Disease Surveillance Center, National Institute of InfectiousDiseases(http://idsc.nih.go.jp/idwr/kansen/k06/k06_(—)41/k06_(—)41.html) (NonPatent Literature 1).

s for measures against schistosomiasis, instructions for the prophylaxisof infection have been made to avoid going barefoot into the habitat ofshellfish as an intermediate host for schistosomes, i.e., a river, apond, etc., and besides, praziquantel (Bayer Yakuhin) is commerciallyavailable as a magic bullet (Non Patent Literature 2). The treatment ofschistosomiasis is basically conducted by single-dose administration ofpraziquantel at 40 mg/kg. It is said that schistosomiasis is cured bythe treatment inmost cases. Acute symptoms (e.g., abdominal pain,diarrhea, mucous and bloody stool, fever, and cough) of schistosomiasisare known as Katayama's fever, and when not being treated, the symptomsare basically relieved and become chronic. Even when Katayama's fever isrelieved by the administration of praziquantel, praziquantel is noteffective against immature schistosomes, and is therefore recommended tobe administered again after 3 months. Praziquantel is also said to haveno prophylactic effect. Meanwhile, Non Patent Literature 1 alsodescribes that it has been reported that artemether, which is one ofartemisinin-based drugs serving as antimalarial drugs, exhibits aneffect on schistosomes at the immature stage and may therefore be usednot only as a therapeutic drug at the early stage of infection but alsofor the prophylaxis of the infection, but that artemether still remainsunpopular. See FIG. 1 for a life cycle of schistosomes and effectiveadministration periods of reported existing drugs.

Even when schistosomiasis is cured by the administration ofpraziquantel, once one suffers from liver dysfunction, the restorationis difficult and liver dysfunction is accumulated through repetitiveinfections. In Japan, as mentioned above, Schistosoma japonicum in thecountry was able to be eradicated by the prevention of infection fromOncomelania nosophora as an intermediate host for schistosomes and theearly detection and treatment of patients. In contrast, wide infectedareas remain in, for example, China, Southeast Asia, and Africa, andreports on the occurrence of resistance to praziquantel also exist.There is no prophylactic means such as a vaccine at present.Accordingly, there is also an international demand for the developmentof a novel antischistosomal agent which may also serve as a prophylacticdrug.

-   [Non Patent Literature 1]    http://idsc.nih.go.jp/idwr/kansen/k06/k0641/k0641.html-   [Non Patent Literature 2] Prescription Drug Package Insert:    praziquantel formulation (Biltricide(R) tablet) manufactured and    sold by Bayer Yakuhin, Ltd. (revised in April, 2005)

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

An object of the present invention is to provide a novelantischistosomal agent, and more specifically, to provide a novel drugcapable of killing schistosomes at the immature stage and inhibiting thegrowth of the schistosomes in vivo to prevent the development of liverdysfunction due to eggs of the schistosomes in the case of infectionwith the schistosomes.

Means for Solving the Problems

The inventors of the present invention have made extensive studies inorder to solve the above-mentioned problem. As a result, the inventorshave found that a peroxide derivative allows the inhibition of thegrowth of schistosomes in vivo to prevent the development of liverdysfunction due to eggs of the schistosomes even in the case ofinfection with the schistosomes. Thus, the present invention has beencompleted.

That is, the present invention includes the following:

1. a novel antischistosomal agent, comprising as an active ingredient aperoxide derivative represented by the general formula (I):

[wherein, C represents an alicyclic hydrocarbon group which may besubstituted, and n represents an integer of 1 to 6];2. a novel antischistosomal agent according to the item 1, in which theperoxide derivative is a compound represented by the general formula (I)wherein C represents an alicyclic hydrocarbon group which may have alower alkyl group as a substituent;3. a novel antischistosomal agent according to the item 1 or 2, in whichthe peroxide derivative is a compound represented by the general formula(I) wherein C represents a 4-tert-butylcyclohexylidene,cyclododecylidene, or adamantylidene group, and n represents an integerof 1 to 4; and4. a novel antischistosomal agent according to any one of the items 1 to3, wherein the peroxide derivative is a compound represented by thefollowing formula (II):

Advantageous Effects of Invention

The administration of the novel antischistosomal agent of the presentinvention on Week 2 (during the second week) after infection withschistosomes leads to a decrease in the number of schistosomes in vivo,and the administration of the novel antischistosomal agent prior to Week6 (the sixth week) after the infection can reduce the egg productioncapacity of schistosomes. Thus, the drug of the present invention can beadministered to humans probably at high risk of infection withschistosomes prior to the symptom onset so as to prevent schistosomiasisand thereby avoid liver dysfunction (liver damage).

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating a life cycle of schistosomes andeffective administration periods of existing drugs.

FIG. 2 is a diagram illustrating a drug dosage regimen to examine aninfluence of a novel antischistosomal agent of the present invention onthe number of schistosomes (Experimental Example 1).

FIG. 3 is a graph illustrating an influence of the novelantischistosomal agent of the present invention on the number ofschistosomes (Experimental Example 1).

FIG. 4 is a diagram illustrating a drug dosage regimen to examine aninfluence of the novel antischistosomal agent of the present inventionon the number of eggs produced (Experimental Example 2).

FIG. 5 are graphs illustrating influences of the novel antischistosomalagent of the present invention on the number of eggs produced(Experimental Example 2).

FIG. 6 are photographs showing influences of the novel antischistosomalagent of the present invention on liver lesions of schistosome-infectedmice (Experimental Example 3).

FIG. 7 is a diagram illustrating a life cycle of schistosomes and aneffective administration period of the novel antischistosomal agent ofthe present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

A novel antischistosomal agent of the present invention may beadministered to individuals suspected of infection with schistosomes.Here, a number of kinds of schistosomes are known as described in thesection of “Background Art” above. The schistosomes are not particularlylimited in the present invention, and preferred examples thereof includeSchistosoma japonicum and Schistosoma mansoni. Regarding theantischistosomal agent of the present invention, dosage schedulesdepending on the life cycle of schistosomes are considered. For example,the administration of the antischistosomal agent on Weeks 1 to 2 afterinfection leads to a decrease in the number of schistosomes in vivo andthe weekly administration of the antischistosomal agent on Weeks 5 to 7after the infection, in particular, the administration of theantischistosomal agent on Week 5 reduces the egg production capacity ofschistosomes. The individuals suspected of infection with schistosomesrefer to, for example, individuals who have ever been to fresh waterregions at risk of infection. Even when symptoms due to infection withschistosomes are not clearly manifested, the exacerbation of thesymptoms due to infection can be prevented in advance by theadministration of the antischistosomal agent of the present invention.

The novel antischistosomal agent of the present invention comprises asan active ingredient a peroxide derivative represented by the followingformula (I):

[in the formula, C represents an alicyclic hydrocarbon ring group whichmay have a substituent, and n represents an integer of 1 to 6].

In the above-mentioned general formula (I), examples of the alicyclichydrocarbon ring group which may have a substituent represented by Cinclude: monocyclic alicyclic hydrocarbon groups having 3 to 12 carbonatoms such as cyclopropylidene, cyclobutylidene, cyclopentylidene,cyclohexylidene, cycloheptylidene, cyclooctylidene, cyclononylidene,cyclodecylidene, cycloundecylidene, and cyclododecylidene groups; andbridged ring or polycyclic alicyclic hydrocarbon groups such asbicyclobutylidene, bicyclooctylidene, bicyclononylidene, norbornylidene,norborenylidene, adamantylidene, and noradamantylidene groups. Of those,monocyclic alicyclic hydrocarbon groups having 6 to 12 carbon atoms oran adamantylidene group is preferred, and a cyclohexylidene,cyclododecylidene, or adamantylidene group is more preferred. Further,examples of the substituent which may be possessed by the alicyclichydrocarbon group represented by C include: linear or branched loweralkyl groups having 1 to 6 carbon atoms such as methyl, ethyl, n-propyl,i-propyl, n-butyl, i-butyl, sec-butyl, tert-butyl or a linear orbranched pentyl group; and linear or branched lower alkoxy groups having1 to 6 carbon atoms such as methoxy, ethoxy, n-propoxy, i-propoxy,n-butoxy, i-butoxy, sec-butoxy, tert-butoxy or a linear or branchedpentyloxy group. Of those, lower alkyl groups are preferred and atert-butyl group is more preferred. Of the compounds of the presentinvention, a preferred compound is a compound represented by the generalformula (I), wherein C represents an alicyclic hydrocarbon group whichmay have a lower alkyl group as a substituent, and a more preferredcompound is a compound represented by the general formula (I), wherein Crepresents a 4-tert-butylcyclohexylidene, cyclododecylidene, oradamantylidene group, and n represents an integer of 1 to 4.

Hereinafter, embodiments of the present invention are described indetail. The peroxide derivative represented by the above-mentionedgeneral formula (I) may be manufactured by the method described in JP2000-229965 A.

Specifically, the peroxide derivative is manufactured by the followingmethod:

[in the formula, C and n have the same meanings as those describedabove, and X represents a halogen atom].

In the above-mentioned reaction scheme, the halogen atom indicated by Xis a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom,preferably a bromine atom or an iodine atom.

<Reaction Step (i)>

This reaction step is performed in accordance with the method describedin J. Org. Chem., 62, 4949 (1997). In other words, a known compound (2)is allowed to react with ozone in an appropriate solvent in the presenceof hydrogen peroxide to afford a bishydroperoxide compound indicated by(3). The solvent to be used in this step is not particularly limited aslong as the solvent is not involved in the reaction. Examples of thesolvent include an ether, tetrahydrofuran, and acetonitrile. Of those,an ether is preferred. 30 to 100% hydrogen peroxide may be used. In thereaction, hydrogen peroxide is used in a 1- to 10-fold molar amount,preferably a 1- to 3-fold molar amount with respect to the compound (2),and ozone is used in a 0.5- to 5-fold molar amount, preferably a 1- to2-fold molar amount with respect to the compound (2). The reactiontemperature is −70 to 20° C., and the reaction time is 5 to 30 minutes.The resultant compound (3) may be easily isolated and purified from areaction mixture by general separation means such as columnchromatography and recrystallization. The compound (3) obtained in theabove-mentioned reaction step (i) may be isolated or not isolated andthen used in the reaction step (ii).

<Reaction Step (ii)>

The compounds represented by the compounds (3) and (4) obtained in theabove-mentioned reaction step (i) are allowed to react with each otherin an appropriate solvent in the presence of a base to afford a compoundof the present invention represented by the general formula (I).Examples of the base to be used in this step include: alkali metalhydroxides such as potassium hydroxide, sodium hydroxide, and cesiumhydroxide; alkali metal alkoxides such as sodium methoxide and sodiumethoxide; and tertiary amines such as triethylamine anddiisopropylethylamine. Of those, cesium hydroxide is preferred. Thesolvent is not particularly limited as long as the solvent is anonaqueous solvent, but is particularly preferably a high polar solventsuch as dimethylformamide or dimethylsulfoxide. Further, each of crownethers such as 18-crown-6 may also be added as a reaction promoter. Inthe reaction, each of the compound (4) and the base is used in a 1- to3-fold molar amount with respect to the compound (3). When a reactionpromoter is used, it is added in a 1- to 10-fold molar amount withrespect to the compound (3). The reaction temperature is 0 to 50° C.,preferably 10 to 30° C., and the reaction time is 1 to 48 hours. Theresultant compound (I) may be easily isolated and purified from areaction mixture by general separation means such as columnchromatography or recrystallization.

Specific examples of the peroxide derivative contained in the novelantischistosomal agent of the present invention include compounds shownin Table 1. Those compounds may be manufactured by the method describedin each of working Examples of JP 2000-229965 A. The peroxide derivativecontained in the novel antischistosomal agent of the present inventionis most preferably the compound (1,2,6,7-tetraoxaspiro[7.11]nonadecane)represented by the following formula (II).

TABLE1 [Chem. 2]

1,2,6,7-Tetraoxaspiro[7.11] nonadecane

1,2,6,7-Tetraoxaspiro[8.11] icosane

1,2,6,7-Tetraoxaspiro[9.11] henicosane

1,2,6,7-Tetraoxaspiro[8.11] docosane

7,8,12,13-Tetraoxaspiro[6.8] tridecane

Spiro[tricyclo[3.3.1.1^(3,7)] decane]2,3′-[1,2,4,5] tetroxocane

The novel antischistosomal agent of the present invention may beadministered through any route such as oral administration, subcutaneousinjection, intravenous injection, or topical administration. Further,the novel antischistosomal agent may be formulated into oralformulations such as powders, tablets, fine granules, pills, capsules,and granules, and parenteral formulations such as ophthalmic solutions,injections, and suppositories, which are generally manufactured usingpharmaceutically acceptable carrier, excipient, and other additives.Examples of the pharmaceutically acceptable carrier, excipient, andother additives include glucose, lactose, gelatin, mannitol, starchpaste, magnesium trisilicate, corn starch, keratin, and colloidalsilica. Additional examples thereof include aids such as a stabilizer, abulking agent, a colorant, and a fragrance. Each of those formulationsmay be manufactured by a known conventional manufacturing method by aperson skilled in the art. The blending amount of the peroxide compoundas the active ingredient contained in the novel antischistosomal agentof the present invention is preferably 0.1 to 100% by weight, morepreferably 0.1 to 80% by weight, suitably 0.1 to 50% by weight. Althoughthe daily dose cannot be generally determined because the dosage variesdepending on, for example, the symptom, body weight, age, and gender ofa patient, it is preferably administered at a dosage of generally 0.1 to1,000 mg, preferably 1 to 600 mg per day for an adult human in oneportion or about two to four divided portions.

EXAMPLES

Hereinafter, effects in the case of administration of the novelantischistosomal agent of the present invention are described by way ofexamples. It goes without saying that the present invention is notlimited to the description of the examples.

Example 1 Preparation of Novel Antischistosomal Agent of PresentInvention

The novel antischistosomal agent of the present invention was preparedby dissolving 120 mg of a peroxide derivative(1,2,6,7-tetraoxaspiro[7.11]nonadecane, formula (II)) obtained bysynthesis according to the method described in Example 1 of JP2000-229965 A in 2 ml of olive oil.

Experimental Example 1 Number of Schistosomes In Vivo

100 μl of the antischistosomal agent of the present invention wereorally administered to mice (BALB/c mice, 5-week-old) infected withschistosomes (Schistosoma mansoni) in accordance with a drug dosageregimen of FIG. 2. As a control, 100 μl of olive oil was administered.On Week 6 after the infection, the mice were sacrificed with an overdoseof anesthetic, and the number of schistosomes recovered was countedunder a microscope.

The results confirmed that the number of schistosomes in a group inwhich the antischistosomal agent was administered on Days 14 and 15after the infection was smaller as compared to that in a group in whichthe antischistosomal agent was administered immediately after theinfection, and was reduced by 86% as compared to the olive oiladministration group as a control (FIG. 3).

Experimental Example 2 Number of Eggs Produced Per Adult FemaleSchistosome

100 μl of the antischistosomal agent of the present invention wereorally administered to mice (BALB/c mice, 5-week-old) infected withschistosomes (Schistosoma mansoni) in accordance with a drug dosageregimen of FIG. 4. As a control, 100 μl of olive oil was administered.On Week 9 after the infection, the mice were sacrificed with an overdoseof anesthetic, and the number of schistosomes recovered and the numberof eggs produced per adult female schistosome were measured. The numberof schistosomes was measured in the same manner as in ExperimentalExample 1, and the number of eggs produced was also counted under amicroscope.

The results confirmed that the number of schistosomes in the case ofadministration of the antischistosomal agent on each of Weeks 5 to 7after the infection was not significantly reduced as compared to that inthe olive oil administration group as a control, whereas the number ofeggs produced per adult female schistosome was reduced by 98% ascompared to that in the olive oil administration group. Also in the caseof administration on Week 5 only after the infection, the number of eggsproduced was reduced by 87% (FIG. 5).

Experimental Example 3 Macroscopic Findings on Liver Lesions inSchistosome-Infected Mice

Viscera of each of the mice of Experimental Example 2 were observedmacroscopically. As a result, liver lesions due to eggs of schistosomeswere observed in the olive oil administration group, whereas few liverlesions were observed in the group in which the antischistosomal agentof the present invention was administered on Week 5 after the infection(FIG. 6). Further, enlargement of spleen was also inhibited. The resultsalso confirmed that the antischistosomal agent of the present inventionwas effective on liver lesions caused by eggs of schistosomes as well.

As described above, the administration of the antischistosomal agent ofthe present invention on Week 2 after the infection led to a decrease inthe number of schistosomes, and the administration of theantischistosomal agent on Week 5 after the infection led to asignificant decrease in the number of eggs produced per adult femaleschistosome. Based on those results, a life cycle of schistosomes andeffects depending on a dosage schedule of the antischistosomal agent ofthe present invention were summarized in FIG. 7. The results confirmedthat the administration of the antischistosomal agent of the presentinvention enabled the reduction in the number of schistosomes and alsothe reduction in the number of eggs produced, prior to the developmentof liver lesions due to schistosomes. It has been confirmed that theantischistosomal agent of the present invention can be prophylacticallyadministered to individuals at risk of infection with schistosomes.

INDUSTRIAL APPLICABILITY

As mentioned in detail above, the administration of the novelantischistosomal agent of the present invention on Week 2 afterinfection with schistosomes leads to a decrease in the number ofschistosomes in a living body, and the administration of the novelantischistosomal agent prior to Week 6 after the infection leads to areduction in egg production capacity of schistosomes. Thus, the drug ofthe present invention, when administered to humans probably at high riskof infection with schistosomes in accordance with the above-mentioneddosage regimen, can inhibit schistosomiasis and prevent the developmentof liver dysfunction. Accordingly, the novel antischistosomal agent ofthe present invention can be utilized as an excellent drug which may beprophylactically administered to individuals at risk of infection withschistosomes.

1. A novel antischistosomal agent, comprising as an active ingredient aperoxide derivative represented by the general formula (I):

wherein C represents a monocyclic alicyclic hydrocarbon group having 3to 12 carbon atoms or an adamantylidene group, which may have a linearor branched lower alkyl group having 1 to 6 carbon atoms as asubstituent, and n represents an integer of 1 to
 6. 2. (canceled)
 3. Anovel antischistosomal agent according to claim 1, wherein the peroxidederivative is a compound represented by the general formula (I) whereinC represents a 4-tert-butylcyclohexylidene, cyclododecylidene, oradamantylidene group, and n represents an integer of 1 to
 4. 4. A novelantischistosomal agent according to claim 1, wherein the peroxidederivative is a compound represented by the following formula (II):


5. A novel antischistosomal agent, comprising as an active ingredient aperoxide derivative represented by the general formula (I), which isused in such a manner that the peroxide derivative is administered twoor four times a week at a dosage of 1 to 1,000 mg on any one or aplurality of weeks selected from Weeks 2 to 7 after infection withschistosomes:

wherein C represents a monocyclic alicyclic hydrocarbon group having 3to 12 carbon atoms or an adamantylidene group, which may have a linearor branched lower alkyl group having 1 to 6 carbon atoms as asubstituent, and n represents an integer of 1 to
 6. 6. A novelantischistosomal agent according to claim 5, which is used in such amanner that the peroxide derivative is administered two or four times aweek at a dosage of 1 to 1,000 mg on Weeks 2 and/or 5 after infectionwith schistosomes.
 7. A novel antischistosomal agent according to claim5, which is used in such a manner that the peroxide derivative isadministered two or four times at a dosage of 1 to 1,000 mg on Week 5after infection with schistosomes.
 8. A novel antischistosomal agentaccording to claim 5, wherein the peroxide derivative comprises aperoxide derivative represented by the general formula (I), wherein Crepresents a 4-tert-butylcyclohexylidene, cyclododecylidene, oradamantylidene group, and n represents an integer of 1 to
 4. 9. A novelantischistosomal agent according to claim 5, wherein the peroxidederivative is a compound represented by the following formula (II):


10. A novel antischistosomal agent according to claim 1, wherein thenovel antischistosomal agent further comprises olive oil.
 11. A novelantischistosomal agent according to claim 10, wherein the novelantischistosomal agent comprises the peroxide derivative in a blendingratio of 120 mg with respect to 2 ml of the olive oil.